The present invention relates to a method of controlling and/or regulating fuel supply, preferably by means of fuel injection, to an internal combustion engine, wherein an injection time interval (t.sub.i) and hence the quantity (m.sub.B) of supply is determined in dependency on at least two engine parameters, such as gas pedal position (.alpha..sub.SP) and rotary speed (n) and thereafter a quantity of air (m.sub.L) is induced through throttling means including an adjustable throttling plate.
Particularly in motor vehicles, internal combustion engines are used operating either with a carburator or with a fuel injection system. These conventional fuel supply systems are air controlled systems. The sucked in quantity of air induced to the engine is predetermined by the position of throttling plate and by the rotary speed of the engine. The quantity of fuel supplied to the engine is subsequently adjusted according to the induced quantity of air. For metering the requisite quantity of air and for the additional metering of the quantity of fuel which depends on the metered amount of air, always require a certain period of time. In such air controlled fuel systems therefore the addition of a dose of fuel trails the induction of the metered quantity of air. This time delay, however, affects in a disadvantageous manner the transition behavior of the engine during a load change.
To avoid this shortcoming, another method has been developed wherein the quantity of fuel is predetermined by the gas pedal and corresponding quantity of air is supplied thereafter. The latter method is designated as a fuel controlled system. In spite of its advantages in comparison with air controlled systems, the fuel controlled system did not prevail in practice, inasmuch an accurate metering of the requisite quantity of air could be realized with considerable technological expenditures only.
The two beforementioned fuel supply systems and their disadvantages which are avoided by this invention, will be now briefly discussed with reference to FIGS. 1 to 4 of the drawing.
The behavior of an air controlled system in a dynamic mode of operation is illustrated in the plot diagram of FIG. 1. Dashed lines represent a constant quantity of fuel m.sub.B, and full lines represent a constant quantity of air m.sub.L. For instance, if effective pressure in a cylinder of the internal combusticn engine is to be raised from a point a to a point b, then by means of the gas pedal the throttle plate must be opened to a certain angular position. As a consequence, the induced quantity of air m.sub.L is increased. Due to the inertia of the system, however, both the quantity of fuel m.sub.B and the rotary speed n of the engine remain momentarily constant. As a result, the effective pressure P.sub.e in the cylinder starts decreasing from the point a along the dashed line representing a constant quantity of fuel and only afterwards it rises along a curve to the desired value at the point b.
In the range of a rich mixture at an air ratio of .lambda.=0.9, during the increase of the effective pressure P.sub.e from point d to point e, the behavior of the engine is better than in the preceding case. It will be seen that the effective pressure P.sub.e continuously increases, as it is desirable.
Nevertheless, in both cases there is the disadvantage that the fuel mixture for a transient period of time becomes lean. During the transition times from a to b or from d to e lean peaks occur in the exhaust gas which cause an increase of noxious components in the exhaust. Therefore an exactly opposite behavior is desired and within the both cases the wetting of the suction pipe with fuel must have increased.
If the effective pressure P.sub.e is to decrease, for example from point a to point c or from d to f than in the case of an air controlled system it is disadvantageous that the mixture is unnecessarily enriched, thus causing in the exhaust gas a peak of concentration of polluting agents.
Hence, the air controlled systems exhibit disadvantages in adjusting the mixture ratio particularly in lean mixtures.
Moreover, in any event detrimental peaks in exhaust gas will occur during the transition to another load condition.
The behavior of a fuel controlled system in a dynamic operation is graphically illustrated in the plot diagram in FIG. 2. Also in this diagram the effective pressure P.sub.e in a cylinder is plotted in dependency of air ratio .lambda. for constant quantities of fuel mB and constant quantities of air m.sub.L.
It will be seen that fuel controlled system behaves on the leaner side of the fuel mixture as it is desirable. In increasing the effective pressure P.sub.e during acceleration, for example from point a to point b, the mixture becomes richer. In lowering the effective pressure P.sub.e during deceleration, for example from point a to point c, the mixture becomes leaner. This behavior has a favorable effect also on the correct wetting of the wall of the suction pipe. Consequently, also the behavior of exhaust gas is improved and concentrations of polluting agents are reduced.
At the rich side of the mixture, approximately at an air ratio of .lambda.=0.9, the short drop of effective pressure P.sub.e during acceleration is with a certain disadvantage.
A fuel controlled fuel supply system therefore is particularly well suited for adjusting the components at the leaner side of the mixture. The detrimental exhaust gas peaks in load changes are substantially lower than in air controlled systems. As mentioned above, however, the realization of fuel controlled systems is substantially more expensive in comparison with air controlled systems.
The behavior of power output of the engine having air controlled system, be it a carburator type, or a fuel injection type system, is illustrated in the plot diagram in FIG. 3. The engine output N is plotted against rotary speed n and in dependency on angular position .alpha..sub.DK of throttle plate. It can be seen that in air controlled systems a very non-uniform driving behavior results at changing power output. For instance one drives uphill at a partial load, that means not with full gas, and consequently if the rotary speed n of the engine drops, then at a constant opening .alpha..sub.DK of the throttle plate the power output N decreases.
In fuel controlled systems there are essentially two possibilities how to determine the quantity of fuel by the position of the gas pedal, namely whether by dosing the quantity of fuel per stroke of the engine piston or per time unit. Since this invention is concerned with the first-mentioned possibility only, the power output characteristics of the latter will be considered below.
In fuel controlled systems in which fuel quantity is determined per time unit, one can adjust a quantity distributing piston via an eccenter by means of the gas pedal. From FIG. 4 it is evident that in such a system the power output N from a certain point decreases with increasing rotary speed n. The motor vehicle then behaves approximately so as if an automatic speed regulator be installed in the engine.
The combination of the two systems for metering fuel in internal combustion engines are also possible. One prior art system of this kind is known from the German publication No. 2,014,633 (assigned to the same assignee). In this known system the quantity of air and the quantity of fuel are controlled simultaneously in dependency on the position of the gas pedal and on the rotary speed of the engine.
From German publication No. 2,431,865 (assigned to the same assignee) a fuel controlled injection system is known in which gas pedal moves via a drag lever, an eccentric ball bearing on the quantity distributing piston and in doing so the injection of a predetermined quantity of fuel is controlled. Simultaneously, the injected fuel quantity is sensed by a potentiometer and applied as a desired value to a regulating amplifier. The regulating amplifier controls via a servo-motor the throttling plate in such a way that an air flow meter feeds back or returns a desired preset value. In this way a correct quantity of air is assigned to the predetermined quantity of fuel. However, since the maximum quantity of air depends also on the rotary speed of the engine, this known arrangement cannot preset any arbitrary desired value by means of the gas pedal. Therefore, there is a rotary speed dependent limit for the presetting of the amount of fuel. This is achieved by means of the drag lever whose limit stop is controlled by a rotary speed dependent setting motor. The construction of this known system is very expensive, particularly due to the large number of necessary sensors and adjustors. In addition, this system necessitates a relatively expensive air flow sensor.
In another known variation of the latter system which is somewhat simpler in construction, the injection time interval is preset by the position of the gas pedal. The throttling plate is adjusted by means of the setting motor in such a way that the quantity of air corresponding to the product of rotary speed and of the injection time interval is sensed at the air mass flow meter. This product must be generated in a control device and is used as a desired value for the regulating circuit. Even this simplified system is still relatively expensive even without regard to the cost of the air flow meter.